Pull-push-type switch

ABSTRACT

A pull-push-type switch having a movable contact coupled by hairpinlike spring means to a pull-push switch shaft and a plurality of pairs of fixed contact strips, which permits the switching of many circuits and is mainly used in association with a variable resistor unit.

i United States Patent [151 3 641 292 Tanuka Feb. 8, 1972 [54] PULL-PUSH-TYPE SWITCH [51] Int. Cl. .110! 15/18 [72] Inventor: Heiroku Tanaka Osaka Japan [58] Field Of Search ..200/67 C, 67 A, 76

[73] Assignee: Matsushita Electric Industrial Co., Ltd., [56] References Cited Osaka, Japan [22] Filed: Nov. 27, 1970 U DSTATES PATENTS 2,967,218 1/1961 DOISCC ..ZOO/7b 93,376 3,402,374 9/1968 Gaines et a]. ..:mm

301 Foreign Application Priority um Primary Examiner-David Smith, Jr.

Nov 28 1969 Japan I l M138 Attorney-Stevens, Davis, Miller & Mosher June 5, i970 Japan... ....45/55s93 June 5, 1970 Japan.... 45/55894 [57] ABSIKACT June 1970 p 55895 A pull-push-type switch having a movable contact coupled by June 1970 p -m 45/55896 hairpinlike spring means to a pull-push switch shaft and a plu- J1me 1970 p n- 45/55397 rality of pairs of fixed contact strips, which permits the June 1970 p switching of many circuits and is mainly used in association June 5, 1970 Japan ..45/55899 with a variable resistor unit,

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sis 522 .PULL-PUSII-TYPE SWITCH This invention relates to improvements in pull-push-type switches, which can be used in association with variable resistors and are capable of closing and opening many circuits.

In the conventional pull-push-type multicontact switch, a movable contact interlocked to a switch shaft makes or breaks many fixed contact pairs as the switch shaft is pulled or pushed. Usually, the construction of this type of switch is complicated, requiring many steps in its manufacture, both in the production of parts and assemblage of the switch resulting in high manufacturing costs. Also, contact failure frequently occurs and reliable switching action cannot be sufficiently ensured with this type of switch.

Accordingly, it is an object of the invention to overcome the above conventional drawbacks by the provision of a novel pull-push-type switch, which is simple in construction and can ensure reliable switching action, and for which the cost of production and assemblage is low.

According to the invention, the pull-push-type switch comprises a hollow insulating switch case open at opposite ends, a plurality of fixed contact strips each having a terminal portion at one end and an intermediate notched portion, said fixed contact strips being fitted in respective grooves formed in pairs in said switch case at opposite ends of said switch case, two contact-insulating lids respectively closing the opposite ends of said switch case and urged against said fixed contact strips, an attachment metal member having a central portion extending across either one of said contact-insulating lids and opposite folded end portions clamping said one of said contact-insulating lids, said contact-insulating lids being secured to said switch case by said attachment metal members, a switch shaft penetrating through one of said contact-insulating lids to the inside of said switch case and provided with a pulleylike sheath member mounted on said switch shaft adjacent to its end inside said switch case, a U-shaped insulating movable member disposed inside said switch case, said switch shaft extending through the space between the legs of said U- shaped movable member, said legs of said U-shaped movable member each having an outwardly extending ear, and a circular contact ring being loosely fitted on each said ear, and a pair of hairpinlike spring members each being in engagement with both of said movable member and said pulleylike sheath member on said switch shaft end, said spring members being adapted to convert the axial pull or push displacement of said switch shaft into a corresponding snapping motion of said movable member to provide the switching action of causing said contact rings to make or break the contact between the corresponding pairs of said fixed contact springs.

With the multicontact construction of the pull-push-type switch described above according to the invention the contact strips constituting the fixed contacts may be produced inexpensively. Also, the reliable making and breaking of the contact between the pairs of fixed contact strips by pulling or pushing the switch shaft can be ensured through the employment of circular contact rings. Further, the assemblage of the switch does not require any caulking or riveting of the fixed contact strips, that have heretofore been involved in the assemblage of switches of this type, and which is a great practical advantage in that the overall cost for the production of parts and assemblage of the switch can be greatly reduced.

The above and other objects, features and advantages of the invention will become more apparent from the following description of the preferred embodiments with reference to the accompanying drawings, in which:

FIG. 1 is a front elevation of an embodiment of the pullpush-type switch combined with a variable resistor in accordance with the invention;

FIGS. 2 and 3 are respectively side and rear elevations of the unit of FIG. 1;

FIG. 4 is an enlarged sectional view of the switch taken along line 4-4 in FIG. 2 rotated 90 clockwise from its position in FIG. 2, and viewed in the direction of the arrows;

FIG. 5 is an enlarged sectional view of the switch and variable resistor taken along line 55 in FIG. 3 and viewed in the direction of the arrows;

FIG. 6 is an enlarged sectional view of the switch, particularly showing the switch contacts, taken along a line 6-6 in FIG. 3 and viewed in the direction of the arrows;

FIG. 7 is an enlarged perspective view showing a switch case and some fixed contact strips in the switch according to the invention;

FIG. 8 is a perspective view showing a U-shaped movable member in another embodiment of the pull-push-type switch according to the invention;

FIGS. 9a, 9b and 9c are respectively front, top and side views of the movable member shown in FIG. 8;

FIG. 10 is a sectional view similar to FIG. 4 showing a further embodiment of the pull-push-type switch according to the invention;

FIG. 11 is an exploded perspective view showing the movable means of the switch of FIG. 10;

FIG. 12 is a sectional view similar to FIG. 4 showing a still further embodiment of the pull-push-type switch according to the invention;

FIG. 13 is an exploded perspective view showing the movable means of the switch of FIG. 12;

FIG. 14 is a fragmentary enlarged perspective view showing a modification of part of the movable means of FIG. 13;

FIG. 15 is an enlarged perspective view showing another example of the insulating spacer mounted on the movable means;

FIG. 16 is a sectional view similar to FIG. 5 showing yetanother embodiment of the pull-push-type switch according to the invention;

FIGS. 17 and 18 are respectively similar to FIGS. 4 and 6 showing the switch of FIG. 16 with FIG. 18 being a sectional view taken along line 18-18 of FIG. 17;

FIG. 19 is a view similar to FIG. 7 showing a switch case and some fixed contact strips in the switch of FIG. 16;

FIGS. 20a and 20b are perspective views showing fixed contact strips and a common fixed contact strip on a yet further embodiment of the pull-push-type switch according to the invention;

FIG. 21 is a sectional view similar to FIG. 6 showing the ordinary and common fixed contact strips of FIGS. 20a and 20b arranged in the switch case;

FIGS. 22 and 23 are circuit diagrams showing respective applications of the switch;

FIGS. 24a and 24b are elevational and axial sectional views respectively showing a sheath mounted on the switch shaft end in the usual pull-push-type switch with FIG. 24b being a sectional view taken on line 24b24b of FIG. 24a;

FIGS. 25a and 25b are end elevational and axial sectional views, respectively, showing a sheath together with the switch shaft end in a further embodiment of the pull-push-type switch according to the invention with FIG. 25b being a sectional view taken on line 25b25b of FIG. 25a;

FIGS. 26a and 26b are end elevational and axial sectional views, respectively, showing the sheath of FIGS. 25a and 25b with FIG. 26b being a sectional view taken on line 26b-26b of FIG. 26a;

FIGS. 27a and 27b are end elevational and axial sectional views, respectively, showing a modification of the sheath of FIGS. 25a and 25b together with the switch shaft end with FIG. 27b being a sectional view taken on line 27b-27b of FIG. 27a;

FIGS. 28a and 28b are end elevational and axial sectional views, respectively, showing the sheath of FIGS. 27a and 27b with FIG. 28b being a sectional view taken on line 28b-28b of FIG. 280;

FIG. 29 is a sectional view showing one leg of the U-shaped movable member in the usual pull-push-type switch;

FIG. 30 is a sectional view similar to FIG. 29 showing part of the movable member in a further embodiment of the pullpush-type switch according to the invention; and

FIG. 31 is a sectional view similar to FIG. 29 showing a modification of the movable member of FIG. 30.

Referring now to FIGS. 1 to 7, reference numeral 1 in FIG. 2 generally designates a pull-push-type switch embodying the invention. It is usually combined with a variable resistor as generally designated by numeral 2 in FIG. 2. The switching action of the switch 1 is provided by pulling or pushing a common shaft 3 (moving the shaft to the right or left in FIGS. 2 and As most clearly shown in FIG. 4, the switch comprises a hollow insulating switch case 4 open at both front and rear ends, inside which the end of the shaft substantially coaxial with the case axis is disposed. Within the switch case 4 is also disposed a U-shaped movable member 5 of an insulating material. The U-shaped movable member 5 has both leg portions formed with respective integral, outwardly extending ears 6 and 6' of an oval cross section. One the ears 6 and 6' are loosely fitted respective circular contact rings 7 and 7'. A pulleylike sheath 8 is fitted on the end of shaft 3 inside the switch case 4. The movable member 5 is linked to the sheath 8 through a pair of U-shaped, hairpinlike spring members9 each having opposite legs, one of which is engaged in a corresponding groove formed in the sheath 8, and the other of which is engaged in an inner groove 34 formed in the corresponding leg portion of the movable member 5.

As most clearly shown in FIG. 7, the switch case 4 is formed with two pairs of aligned grooves 10, 10' and 11, 11' across opposite sidewalls at one end of the hollow case. Similar grooves 12, 12 and 13, 13 (grooves 12' and 13 being unseen in FIG. 7) are also formed at the other end in alignment with the respective grooves 10, 10' and 11, 11'. Eight contact strips 18, 18', 19, 19', 20, 20', 21 and 21 each having an intermediate notch 14, 14', 15, 15, 16, 16, 17 or 17 (notches 15, 15, 17 and 17' not being shown) are mounted in the respective grooves 10, l0, 11, 11', 12, 12', 13 and 13 formed in the switch case 4. The notch serves to restrict the lengthwise movement of the contact strip when it is fixed to the switch case.

As most clearly seen in FIG. 5, the opposite open ends of the switch case are closed by respective insulating lids 22 and 23, which are urged against the respective contact strips, that is, the lid 22 is urged against the contact strips 18, 18, 19 and 19 and the lid 23 against the contact strips 20, 20', 21, 21, and securely attached to the switch case by U-shaped metallic attachment member 24, which is secured in variable resistor case 28 and is provided at its opposite, open end with tabs 25, 25" and 25" which are folded over lid 22 to clamp switch 1 to resistor 2. The width of the intermediate notched portion of the contact strips is designed to be slightly greater than the depth of the grooves formed in the switch case 4, so that the insulating lids 22 and 23 are urged against the edges of the contact strips slightly projecting from the ends of the switch case. Thus, the contact strips are securely fixed in the switch case 4.

The contact strips constitute fixed contact parts 18, 18 to 21, 21. The facing ends of the contact strips in pair are disposed in the neighborhood of each other within the switch case 4, with their opposite ends extending outside the switch case, as shown in FIGS. 4 to 6. As most clearly shown in FIG. 6, each of the contact strips has its inner end beveled.

The switch case 4 is formed with inner shouldered portions 26, 26', 27 and 27' serving to determine the lateral position of the movable member 5, as shown in FIG. 4.

As shown in FIGS. 2 and 5, the switch case 4 is secured to a variable resistor case 28 made of a metallic or other material. The open front end of the variable resistor case 28 remote from the switch case 4 is closed by a front plate 29, which carries a bearing 30, in which is journaled the common shaft 3. The shaft 3 is axially slidable and rotatable in the bearing 30. Only the rotation of the common shaft 3 is transmitted to a slide holder 31, which is coupled to the shaft 3 and is disposed inside the variable resistor case 28. A slide 32 mounted on the slide holder 31 rotates with the holder 31 while maintaining sliding contact with a resistor 33 secured to the front plate 29. As its central portion is always in contact with a contact plate (not shown) electrically connected to a slide terminal, the resistance between a fixed terminal connected to the resistor 33 and the slide terminal is varied with the rotation of the com mon shaft 3.

The pull-push-type switch 1 described above according to the invention operates as follows.

When the switch shaft 3 is pushed, the switch state as shown in FIG. 5 results. When the switch shaft 3 is pulled from this state to the right, the movable member 5 is displaced from right to left by the spring action of the hairpinlike springs 9. On the other hand, by pushing the switch shaft 3 to the left the movable member 5 is moved from left to right. The springs 9 at this time provide a nodal character to the movement of the switch shaft 3 being pulled or pushed while at the same time causing the snapping motion of the movable member 5 to the left or right in FIG. 5 (in the direction of axis of the switch shaft 3).

With the snapping motion of the movable member 5, as the switch shaft 3 is pushed for instance, the circular contact rings 7 and 7', which are fitted on the respective ears 6 and 6' projecting from the legs of the movable member 5, are shifted in the axial direction by the ears 6 and 6' integral with the movable member 5 and forcibly urged by these ears against the respective pairs of fixed contact strips 18, 18 and I9, 19', as indicated by dashed lines in FIG. 6, thus making contact between the contacts 18 and 18 and between the contacts 19 and 19'. With the snapping motion of the movable member 5 in the opposite direction, as the switch shaft 3 is pulled this time, the contact rings 6 and 6 are shifted in that direction and forcibly urged against the respective pairs of fixed contact strips 20, 20' and 21, 21, as indicated by solid lines, thus making contact between the contacts 20 and 20 and between the contacts 21 and 21.

It is to be appreciated that the displacement of the contact ring 7 or 7 in the direction of axis of the switch shaft 3 is comparatively small, only between opposite pairs of contact strips 18, 18' and 19, 19 or between opposite pairs of contact strips 20, 20' and 21, 21'. Also, the facing ends of the contact strips in pair are rounded or beveled as mentioned earlier, which is very convenient for the contact rings to secure contact with these contact strips. Further, the contact rings 7 and 7 are loosely fitted on the respective ears 6 and 6', whichare oval in cross section. Thus, even if the movable member 5 tends to undergo a slight lateral deviation during its snapping motion, the contact rings 7 and 7' can roll on the beveled end of the contact strips, so that the contacts 18 and 18, 19 and 19', 20 and 20, and 21 and 21 may be made reliably and held stably. Furthermore, as is apparent from the Figures, the contact strips are of the same configuration and dimensions, so they may be produced by the same mold.

In the preceding embodiment, circular contact rings 7 and 7 are fitted on oval ears 6 and 6' outwardly protruding from the legs of the movable member 5. Since the contact rings 7 and 7 are circular and the cross section of the ears 6 and 6' is oval, the movable member 5 tends to rotate if the spring forces of the hairpinlike springs 9 exerted on the movable member 5 becomes unbalanced. Sometimes, the movable member 5 will tilt about the ears 6 and 6', obstructing the motion of the movable member 5 in the direction of axis of the switch shaft 3. On extreme occasions, the spring 9 will be detached from the spring detention groove 34 formed in the corresponding leg of the movable member 5. In such cases, normal switching action cannot be efiected.

FIGS. 8, 9a, 9b and 9c show a modification of the movable member 5, which overcomes the above drawbacks. In these Figures, parts like those described above are designated by like reference numerals. The modified movable member 5 is provided with perpendicular projections 35 and 35' extending in opposite directions from its central portion.

With the modified movable member 5 substituting for the one previously described, the projection 35' will be in engagement with the insulating lid 23 closing the front open end of the switch case 4 when the contact rings 7 and 7 are respectively making contact between the contact strips 20 and 20 and between the contact strips 21 and 21', while the projection 35 will be in engagement with the insulating lid 22 closing the front end of the switch case 4 when the contact rings 7 and 7 are respectively making contact between the contact strips 18 and 18' and between the contact strips 19 and 19'. Thus, the movable member 5 may be held parallel to these insulating lids 22 and 23. The ears 6 and 6' protruding from the respective legs of the movable member 5 and either one of the projections 35 and 35' form a three-point support to hold the movable member 5 parallel to the insulating lids. To realize this three-point support, it is necessary that the end of the leg of each hairpinlike spring 9 received in the spring detention groove 34 in the corresponding leg of the movable member 5 is sufficiently apart from the end of the corresponding leg of the movable member such that the spring force is exerted on the movable member at a point substantially midway between the center line through the ears 6 and 6' and a line parallel thereto and passing a point underneath the projection 35.

The modified movable member 5 described above is provided with the two perpendicular projections 35 and 35' extending in opposite directions from its central portion. Alternatively, a single perpendicular projection extending towards one of the insulating lids 22 and 23 may be provided on the central portion of the movable member 5, and a support member to be engaged by the movable member 5 may be provided on the other insulating lid. Of course, the support member may not necessarily be provided on either one of the insulating lids 22 and 23 but it may be provided on the switch case 4 as well. The cross section of the projections 35 and 35' may be circular or of any other suitable shape.

In the preceding embodiments, the contact rings 7 and 7 loosely fitted on the respective ears 6 and 6' of the movable member 5 are likely to touch the corresponding walls of the switch case 4. With this construction, in course of prolonged use of the switch it is possible that the insulation between contact strips 18 and 18, 19 and 19, 20 and 20', and 21 and 21' will be degraded. This is because of the fact that, due to wear, conductive material powder, mainly carbon, which is produced by the arcing occurring at the contact points when the contact rings 7 and 7' is detached from the associated contact strips, accumulates on the inner wall surfaces of the switch case 4 frequently contacted by the contact rings 7 and 7. Therefore, if the pull-push-type switch of the above construction is used as a power source switch for a power supply providing a large current as in a television set, unexpectedly large current would flow even with the switch in the off" state, an extremely dangerous condition.

FIGS. and 11 show a further embodiment of the pullpush-type switch, in which a measure is taken to eliminate the above problem. In the Figures, like parts as those already described are designated by like reference numerals. In this embodiment, improvements are made in the structure of the movable member 5, more particularly its ears 6 and 6 which are cylindrical and are provided with grooves 135, 135, respectively. The movable member 5 in this embodiment is similar to the ones in the preceding embodiments in that it carries the contact rings 7 and 7' loosely fitted on the respective ears 6 and 6' protruding from its legs. In this embodiment, however, washers 134 and 134' are fitted on the respective ears 6 and 6 adjacent the outer side of the respective contact rings 7 and 7. The washers 134 and 134' are fitted in annular grooves 135 and 135' respectively formed in the ears 6 and 6' to define or leave respective marginal end portions 136 and 136' of the ears 6 and 6' facing the corresponding inner wall surfaces 137 and 137' of the switch case 4.

With this construction, though the end portions 136 and 136 of the respective ears 6 and 6 might touch the corresponding inner wall surfaces 137 and 137' of the switch case 4, the contact rings 7 and 7' and the washers 134 and 134' will never touch the inner surfaces of the switch case 4. Since the contact rings 7 and 7' are thus held apart from the inner wall surfaces 137 and 137 of the switch case 4, the contamination of the inner wall surfaces with conductive material powder due to wear will never result in degradation of the insulation between the contact strips 18 and 18', 19 and 19, 20 and 20', and 21 and 21'. Thus, the problem of accidentally causing a large current to fiow with the switch in the open state can be totally overcome.

FIGS. 12 and 14 show a still further embodiment, which is an alternative to the previous embodiment. In the Figures, parts like those already encountered are designated by like reference numerals. In this embodiment, consideration is also paid to the structure of the movable member 5 having ears 6 and 6' carrying contact rings 7 and 7'. Like the preceding embodiment, the movable member 5 in this embodiment is similar to those in the previous embodiments insofar as it carries the contact rings 7 and 7' loosely fitted on the respective ears 6 and 6' protruding from its legs. In this embodiment, however, insulating spacers 235 and 235' are fitted on the respective ears 6 and 6 adjacent the outer side of the respective contact rings 7 and 7. The insulating spacers 235 and 235' each are stepped and have a large-diameter portion and a small-diameter portion. Either the ends 234 and 234' of the small-diameter portions of the insulating spacers 235 and 235' or the ends of the ears 6 and 6' are adapted to touch the corresponding inner wall surfaces 236 and 236' of the switch case to restrict the movement of the movable member 5 in the widthwise direction within a predetermined range. V

With this construction, the insulating spacers 235 and 235' effectively separates the respective contact rings 7 and 7 from the corresponding inner wall surfaces 236 and 236' of the switch case 4. Since the contact rings 7 and 7' are held apart from the inner wall surfaces 236 and 236 of the switch case 4, the contamination of the inner wall surfaces with conductive material powder due to wear will never give rise to degraded insulation between the contact strips 18 and 18', 19 and 19', 20 and 20', and 21 and 21' that would otherwise result from the frequent contact of the contact rings 7 and 7' with the contaminated inner wall surfaces of the switch case 4. Thus, the problem of accidentally causing large currents while the switch is open can be absolutely overcome.

The insulating spacers 235 and 235' may not be necessarily stepped but may have a uniform outer diameter, as shown in FIG. 15.

The preceding embodiments still have a significant problem. In the switches as described in the foregoing, there is a slight gap between the fixed contact strips 18, 18', 21' on one hand and the grooves 10, 10', 13' on the other hand due to the tolerance of the thickness of the former and the tolerance of the width of the latter. Strictly speaking, there is also a gap between the insulating lids 22 and 23 urging the fixed contact strips on one hand and the fixed contact strips on the other hand. These gaps give rise to a capillary phenomenon. The flux used in soldering terminal leads (not shown) to the terminal portions of the fixed contact strips 18, 18', 21 is pulled through these gaps, and sometimes it reaches the contact portions, inviting the contact failure of the switch.

FIGS. 16 to 19 show yet another embodiment of the pullpush-type switch, in which a measure is taken to prevent the migration of the fiux and the eventual contact failure of the switch. In these figures, like parts as already referred to are designated by like reference numerals. Particularly, FIG. 16 corresponds to FIG. 5, FIG. 17 to FIG. 4, FIG. 18 to FIG, 6, and FIG. 19 to FIG. 7.

As most clearly seen from FIG. 19, this embodiment is different from the preceding embodiments in that the width of the grooves 10, 10', 11, 11',12, 12', 13 and 13' formed at opposite open ends of the switch case 4 for receiving the respective notched portions 14, 14', 15, 15', 16, 16, 17 and 17' of the contact strips 18, 18', 19, 19', 20, 20', 21 and 21' is increased along an intermediate portion of the individual grooves by symmetrically cutting the intermediate portion of opposite sidewalls of each of the grooves to define respective recesses 334, 334', 335, 335', 336, 336, 337 and 337 (recesses 337 and 337' being unseen), and that the contact strips 18, 18, 19, 19', 20, 20, 21 and 21 are formed with respective notches 338, 338', 339, 339, 340, 340', 341 and 341' (notches 341 and 341 being not shown) along the edge opposite the notches 14, 14', 17, that is, along the edge in contact with the associated one of the insulating lids 22 and 23, and conforming in position to the corresponding recesses, while it is similar to the preceding embodiments so far as the grooves 10, 10', 13' receive the notched portions l4, l4, 17 of the respective contact strips 18, 18', 21' urged by the associated insulating lids 22 and 23.

With this construction, where the notched portions 14, 14,

. 17 of the fixed contact strips 18, 18', 21' each are surrounded by the space of a U-shaped cross-sectional configuration defined by the notches 338, 338', 341 formed along the edge of the contact strips in contact with the associated insulating lids 22 and 23 and the recesses 334, 334', 341' wider than the thickness of the contact strips and as deep as the lateral dimension of the notched portion of the contact strips, the flux will migrate through switch case openings around the fixed contact strips l8, 18', 19, 19', 20, 21 and 21' only up to the said U-shaped space and cannot reach the contact portions. Thus, the contact failure of the switch due to the migration of the flux may be prevented.

FIGS. 20a, 20b and 21 show a yet further embodiment of the pull-push-type switch. This embodiment uses one or more modified (or common) fixed contact strips each having a terminal portion at one end and two contact portions at the other end. FIG. 20a shows ordinal fixed contact strips 18 and 20, and FIG. 20b shows a modified (or common) fixed contact strip 424. These ordinary and common fixed contact strips may be arranged as shown in FIG. 21. The Figure shows the switch with the switch shaft in the pushed state.

The preceding embodiments still present another significant problem. The construction of the sheath at the end of the switch shaft in the preceding embodiments is not very different from the conventional pull-push-type switch.

FIGS. 24a and 24b show a typical example of the sheath construction employed in the conventional pull-push-type switch, to which the invention pertains. A sheath 514 having a peripheral spring-receiving annular groove 513 is mounted on an end, reduced diameter portion 512 of switch shaft 511. Received in the spring-receiving groove 513 are one end portions of U-shaped springs 516 in pair having their other end portions received in respective spring detention places in the movable body 5 (not shown). The switch shaft is formed with annular grooves 517 and 518, in which washers 519 and 520 are respectively secured.

Usually, in the pull-push-type switch arcing is produced at the time of making and braking contacts. Particularly, a heavy spark is produced when breaking contacts. The spark thus produced sometimes reaches the switch shaft 511 and the washer 519 secured at the end thereof. At such instances, the switch shaft 511 is momentarily short-circuited, since it is usually grounded as a nonchargeable metallic part.

The production of a spark reaching the switch shaft 511 or Washer 519 will present no practical problem, if the pull-pushtype switch is inserted in a circuit as shown in FIG. 22. However, if the switch is inserted in a circuit as shown in FIG. 23, the arcing between the switch contacts on one hand and the switch shaft 511 is equivalent to short-circuiting the power source 501 to ground, so that an unexpectedly large current is accidentally caused, thus breaking the fuse, causing damage to the switch contacts or to the switch shaft 511 or sometimes causing combustible switch parts to catch fire and be damaged.

The above undesired phenomenon does not take place if the space in the neighborhood of the spark-producing spot is free from any grounded nonchargeable metallic part. It was experimentally found that no practical problem arises if the gap between the contacts, between which the spark is produced, is

sufficiently separated from the grounded nonchargeable metallic part, and that the above phenomenon can be prevented to some extent by reducing the intensity of the spark with a suitable different contact material.

However, the power source switches for such appliances as television sets are mostly combined with a variable resistor and are attached to the back thereof, and their size is desired to be substantially equal to the size of the associated variable resistor. Also, the antispark contact material is quite expen sive. Therefore, A switch construction providing a sufficiently large separating zone is difficult and the selection of the contact material is subject to restrictions from the economical point of view.

FIGS. 25a, 25b, 26a and 26b show a further embodiment of the pull-push-type switch according to the invention. In this embodiment, improvements are made in the structure of the end of the switch shaft. Referring to these Figures, reference numeral 521 in FIG. 25b designates the switch shaft, which is a nonchargeable metallic part as mentioned above. The switch shaft 521 is provided with a substantially cylindrical, antispark sheath 522 made of an antispark plastic insulating material, The antispark sheath 522 has an intermediate, reduced inner diameter portion 523 fitted on an end, reduced diameter portion 524 of the switch shaft 521, a large diameter portion at its one end sheltering the end of the switch shaft 521 and a washer 525 fitted thereon and a medium inner diameter portion 527 at its other end accommodating the diameter of the switch shaft 521. Similar to the sheath of FIGS. 24a and 24b, the antispark sheath 522 is formed with a peripheral annular spring-receiving groove 528 receiving one end portions of two U-shaped springs 529 having other end portions tied to a movable body (not shown), which is disposed within a switch case (not shown) and movable in the direction of axis of the switch shaft 521.

FIGS. 27a, 27b, 28a and 28b show a modification of the preceding embodiment. In the Figures, parts like those in the preceding embodiment are designated by like reference numerals. This modification is suited where restrictions are imposed on the diameter of the large diameter portion 526 accommodating the washer 525 so that the washer 525 cannot be secured on the end of the switch shaft 521. In this modification, an antispark sheath 522 has an elongate groovelike traversable washer accommodating section 530 defined by opposite antispark shelter walls 531. The washer 525 can be fitted by inserting it into the washer-accommodating section from between the opposite antispark shelter walls 531. Unlike the annular spring-receiving groove 528 in the preceding embodiment, the switch shaft 521 in this modification is formed with two parallel straight spring-receiving grooves 528', which are also parallel to the groovelike washer-accommodating section 530. The spring-receiving grooves 528' are made parallel to the washer-accommodating section 530 to the end that the antispark shelter walls 531 face the spark-producing sites of the contacts. Since the rotation of the antispark sheath 522' is restricted by the urging springs 529, the sheath S22 is always held at a constant angular position with respect to the sparkproducing sites irrespective of the rotation of the switch shaft 521.

With the construction described above where the switch shaft, a nonchargeable metallic part, and the washer fitted thereon are sufficiently sheltered from spark-producing sites by an antispark sheath of an antispark plastic insulating material, the short circuit between the spark-producing site of the contacts and the switch shaft may be prevented, even if the spark from the spark-producing site reaches the proximity of the switch shaft. Besides, this construction requires no substantial alteration of the design of the usual pull-push-type switch and may be readily put into practice. Also, reliable switch function can be expected. Further, the sheath construction described above provides a great practical benefit from standpoint of cost, since it requires no fundamental alteration of the design of the usual pull-push-type switch, merely requiring the substitution of the antispark sheath, whereby the switch may be duly qualified for large current applications. 

1. A pull-push-type switch comprising: a hollow insulating switch case open at opposite ends; a plurality of fixed contact strips each having a terminal portion at one end and an intermediate notched portion, said fixed contact strips being fitted in respective grooves formed in pairs in said switch case at opposite ends of said case; two contact-insulating lids respectively closing the opposite open ends of said switch case and urged against said fixed contact strips; attachment metal member having a central portion extending across either one of said contact-insulating lids and opposite folded end portions clamping said one of said contactinsulating lids, said contact-insulating lids being secured to said switch case by said attachment metal member; a switch shaft penetrating through one of said contactinsulating lids to the inside of said switch case and provided with a sheath member mounted on said switch shaft adjacent the end thereof inside said switch case; a U-shaped insulating movable member disposed inside said switch case, said switch shaft extending through the space between the legs of said U-shaped movable member, said legs of said Ushaped movable member each having an outwardly extending ear, and a circular contact ring being loosely fitted on each said ear; and a pair of hairpinlike spring members each being in engagement with both said movable member and said pulleylike sheath member on said switch shaft end, said spring members being adapted to convert the axial pull or push displacement of said switch shaft into corresponding snapping motion of said movable member to provide the switching action of causing said contact rings to make or break the contact between the corresponding pairs of said fixed contact strips.
 2. The pull-push-type switch according to claim 1, wherein said U-shaped movable mEmber has two perpendicular projections extending in opposite directions from the central portion of said movable member, each said projection being adapted to engage the corresponding one of said contact-insulating lids.
 3. The pull-push-type switch according to claim 1, wherein said U-shaped movable member has a perpendicular projection extending from the central portion of said movable member, and the side of said central portion of said movable member opposite said projection is adapted to engage a support member provided on either the contact-insulating lid not engaged by said projection or said switch case.
 4. The pull-push-type switch according to claim 1, wherein said ears of said movable member each are fitted with a washer on the side of each said contact ring nearer the corresponding sidewall of said switch case to leave a marginal end portion of each said ear.
 5. The pull-push-type switch according to claim 1, wherein said ears of said movable member each are fitted with an annular insulating spacer on the side of each said contact ring nearer the corresponding sidewall of said switch case.
 6. The pull-push-type switch according to claim 1, wherein said switch case has recesses respectively formed by symmetrically cutting the intermediate portion of opposite sidewalls of said individual fixed contact strip receiving grooves corresponding to the central portion of said fixed contact springs to increase groove width along said intermediate portion, said recesses having the same depth as the lateral dimension of said fixed contact springs, and said fixed contact springs each having a notch on the side nearer the associated contact-insulating lid, said notches respectively conforming in position to said recesses.
 7. The pull-push-type switch according to claim 1, wherein some of said fixed contact strips in pairs are replaced with respective common fixed contact strips each having a terminal portion at one end, an intermediate notched portion and two contact portions at the other end.
 8. The pull-push-type switch according to claim 1, wherein said sheath member mounted on said switch shaft is made of an antispark plastic insulating material and shelters the end of said switch shaft and a washer fitted at the end of said switch shaft.
 9. The pull-push-type switch according to claim 1, wherein each leg of said U-shaped movable member is formed with an inner spring member detention grooved portion provided with a spring member detachment prevention means in the form of a wall bridging the groove or of mutually facing ridges. 